Hydrofoils are carriage wings provided at the lower hull of marine vessels for carrying the vessel over the water so as to prevent or minimize water contact of its' underwater hull surface resulting in a reduction of drag forces originating from water contact therewith thereby speeding up the vessel, reducing fuel consumption and providing for more stable travel. Conventionally, hydrofoils are statically mounted at the lower surface of hulls and consequently cannot be retracted.
Barry et al in U.S. Pat. No. 5,134,954 describes a pair of asymmetric hydrofoil assemblies mounted with a marine vessel. Each asymmetric hydrofoil assembly includes a motor and propeller connected to one end of the associated hydrofoil and the other end pivotally connected to the marine vessel. While the first pair of hydrofoils are symmetrically mounted on opposite sides of the marine vessel, Berry considers this arrangement to be an asymmetric because the motors and propellers are not disposed at the mid-point of their respective hydrofoils.
More recently Ulgen in U.S. Pat. No. 8,051,793 has proposed a retractable hydrofoil for marine vehicles. The retractable hydrofoils are mounted in symmetrical pairs on either side of the hull and are connected to sliding means enabling the hydrofoils to rotate vertically to a retracted position.
For over a century, hydrofoils have been known to be more hydrodynamically efficient than planing hulls but their disadvantages, including complex additional structures and a tendency to snag, have precluded their widespread adoption with the exception of niche markets including some sailing craft and smooth water surface piercing ferries.
Consequently, a need continues for retractable hydrofoils which can easily be retrofitted on conventional marine vessels and other amphibious vehicles and which retract from an operational configuration to a stowed configuration conformably with the hull. By mounting the foils conformally with the hull, we retain the simplicity of a smooth hull bottom when stowed, while gaining the efficiency advantage of high aspect ratio composite hydrofoils when deployed. The weight and cost of the propulsion system and the carbon footprint are nominally halved while the craft range is doubled. Additionally when the retractable hydrofoil is in an operational configuration, the hydrofoil is anhedrally positioned with respect to the horizontal plane of marine vessel. In aerodynamics anhedrally positioned wings are known to increase the maneuverability of high performance jet plane. When the hydrofoils are retracted to a stowed position conformally with the hull of the marine vessel, the marine vessel operates as a conventional marine vessel.